The present invention relates to a digitizer system and, more particularly, but not exclusively to a tracking window for a digitizer system.
A digitizer is a computer associated input device capable of tracking user interactions. In most cases the digitizer is associated with a display screen to enable touch or stylus detection.
U.S. Pat. No. 6,690,156, entitled “Physical Object Location Apparatus And Method And A Platform Using The Same”, assigned to N-trig Ltd., and U.S. patent application Ser. No. 10/649,708, entitled “Transparent Digitizer”, filed for N-trig Ltd., describe a positioning device capable of detecting multiple physical objects, preferably styluses, located on top of a flat screen display. One of the preferred embodiments in both of these documents describes a system built of transparent foils containing a matrix of vertical and horizontal conductors. The stylus is an electromagnetic stylus, which is triggered by an excitation coil that surrounds the foils.
The exact position of the stylus is determined by processing the signals that are sensed by the matrix of horizontal and vertical conductors.
Other known digitizer systems include various physical objects responsive to an electromagnetic signal, such as gaming pieces. For example, gaming tokens comprising a resonant circuit, as described in U.S. Pat. No. 6,690,156, entitled “physical object location apparatus and method and a graphic display device, using the same”, assigned to N-trig Ltd.
U.S. Pat. No. 4,878,553, entitled “Position detecting apparatus”, assigned to Wacom Inc., describes a system comprising a set of conductive loops arranged in rows and columns. The loops are excited periodically, one at a time, in order to sense the presence of an electromagnetic stylus at the surface of the device. In order to detect the stylus presence in the Y direction, each loop on the X axis is excited sequentially in the stylus resonance frequency. Then the digitizer samples all the loops on the Y axis to determine the stylus location. The process is similar for determining the stylus location on the X direction.
U.S. patent application Ser. No. 10/757,489, entitled “Touch detection for a digitizer”, assigned to N-trig Ltd., describes three methods of touch detection using a matrix of conductive antennas. In one embodiment, touch detection is performed by providing periodic excitation of the antennas on one axis using an AC signal, while the antennas on the perpendicular axis are sampled. When a conductive object, such as the user finger, touches the surface of the device a phenomena called trans-conductance occurs. The touch serves as a conductor coupling two adjacent lines transferring the oscillating signal from one conductor to the other.
One of the major drawbacks in the above digitizers is that larger sensing areas require a greater number of antennas\conductive loops in order to maintain the same level of resolution and performance. The fact that the antennas\conductive loops are excited one at a time prolongs the required detection time, thus limiting the update rate and digitizer performance and increasing the cost of the digitizer.
The amount of time taken for calculating the object location linearly increases with the amount of antennas\conductive loops\sensing elements constructing the sensor.
Reference is now made to FIG. 1 which illustrates a prior art position detecting apparatus, described in U.S. Pat. No. 4,878,553, referenced above. Sensor 100 comprises a set of conductive loops arranged in rows 102 and columns 103. The loops are excited periodically, one at a time, in order to sense the presence of an electromagnetic stylus 104 at the surface of the device. In order to detect the stylus presence in the Y direction, each loop on the X axis 102 is excited sequentially in the stylus resonance frequency. Then the digitizer samples all the loops on the Y axis 103 to determine the stylus location. The process is similar for determining the stylus location on the X direction. For example, when the stylus is within the range of an excited loop 105, it is charged with electromagnetic energy. The resonating stylus induces an electrical signal 106 on the perpendicular loop 107.
Consider a sensor of an area A1, comprising X1 conductive loops on the X axis 102, and Y1 conductive loops on the Y axis 103. In this case the stylus location is determined by (X1+Y1) steps. The larger the sensor area, the more conductive loops are required in order to detect the stylus without compromising the resolution level of the sensor.
As demonstrated in the above example, an increase in the number of conductive elements leads to a linear increase in detection time. The increased detection time reduces the digitizer update rate, thus limiting its performance. Furthermore, the large amount of sampling leads to an increase in the need for electronic components and computation power. These are typical problems in all digitizer systems relying on periodic excitation and/or sampling in order to detect a physical object.
A method of touch detection using a matrix of conductive antennas is described in U.S. patent application Ser. No. 10/757,489, referenced above. In order to determine the touch position the antennas are continuously excited using an AC signal. In the presence of touch the sampled electrical signal is attenuated. This detection technique involves only one sampling and excitation step per axis. However, a large amount of processing is required because all the antennas are taken into account.
There is thus a widely recognized need for, and it would be highly advantageous to have, a digitizer system devoid of the above limitations.